1. Field of the Invention
The present invention relates to a mirror formed on a plastic substrate, the mirror being for use primarily in automotive applications and having means to be mounted to a mounting device.
2. Description of the Related Art
Conventional glass mirrors for automotive use are heavy (especially with the trend towards larger mirrors), tend to be difficult to form aspheric or complex shapes, and are prone to shatter in the case of accidents. The replacement of glass with a plastic substrate would offer the ability to reduce weight, mould complex shapes, integrate retention features on the rear surface of the substrate, and achieve a high level of impact resistance. However, plastic substrates tend to be soft, would be readily damaged by UV radiation, heat and water, and would have a propensity towards causing the reflective surface to craze. In addition to the softness problems that would expect to be introduced by the use of a plastic substrate for mirrors, some reflective layers typically used for mirrors (of any type) that are formed from direct metal deposition (such as of aluminium or silver) also themselves tend to be soft. To minimize this problem with glass substrates, most reflective layers are conventionally applied to the rear surface. However, for reflective metals such as chromium, which are harder and more resistant to the elements by virtue of their chemical and mechanical properties, these metals are predominantly applied to the front surface of glass substrates. However, if this were attempted with a plastic substrate, it would be expected that the reflective coating would exhibit crazing, which would be made worse in durability testing such as thermal cycling, and which would likely also fail other standard tests such as a salt spray test. In the case of plastic mirrors, the reflective layer could be applied to the rear or front surface and a hard coating applied in order to provide environmental exposure protection of the plastic substrate and the reflective coating, whilst providing improved abrasion resistance. However, for an automotive application, a rear surface plastic mirror has not been regarded as suitable as it would be interrupted by any retention/clipping features on the rear of the mirror. Also, in the case of an applied hard coating, interference bands would be present which are cosmetically unacceptable. It would thus be desirable to manufacture a plastic mirror, suitable for automotive applications, which does not craze, which does not have interference fringes and which passes the normal automotive tests such as a salt spray test, thermal cycling and shock tests, and accelerated weathering tests. This type of plastic mirror is known from the not published application AU2009906281.
To implement retention clipping features in the plastic glass substrate is one of the big advantages of plastic mirrors. To use clips in plastic substrates is known from EP2112022. However, the clips described in the document face some problems. If a glass backing plate or another plastic support in a one piece mirror or a glass angle actuator is pressed against the plastic substrate and the clips, stress occurs and influences the reflective appearance of the surface. The stress in the soft plastic material results in visible distortion of the reflective surface which is not acceptable.